Our ongoing campaign analysis has revealed that Dridex malware’s latest campaign focus has strongly shifted in recent months from U.K. banks, which had been the main targets previously, to US banks today. Dridex and its latest trends are constantly monitored in our lab, which allowed us to take note when many new targets were recently added to the target list. Redirects to fake pages were most common with U.K. bank incidents. Now the malware mainly uses classical webinjects alongside the redirection technique.

The latest campaign is marked as Botnet 301, version 196810.

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Figure 1: Dridex botnet information

The Dridex target list was significantly expanded (129 redirect and injection directives), mainly focusing on U.S. financial institutes, form-grabbing targets on social media sites (which are also related to the United States), credit card companies, and financial investment corporations.

The most noticeable observation in the current webinjects is that most of them are accompanied by activating the VNC functionality, which enables the fraudsters to remotely connect to their victim during the credentials theft.

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Figure 2: Dridex 301 targeted Institutions by country

New form-grabbing targets

Dridex also steals credentials for non-financial accounts, both over HTTP communication and HTTP over SSL (HTTPS) encrypted communication:

Grabber

Figure 3: Dridex 301 form grabbing of social media information

There have been several targets, including:

· Yahoo

· Microsoft

· Skype

· Twitter

· AOL

· Facebook

How Dridex initiates VNC communication

VNC research conducted by malware researcher Hadas Dorfman

Dridex continues using the VNC functionality in order to remotely connect to machines to facilitate the committing of fraudulent transactions.

The VNC is used inside the redirection mechanism, which was described in our previous blog post, Dridex Botnet 220 campaign.

The following is a snippet of a classical Dridex webinject:

classical webinject

Figure 4: Dridex 301 classical webinject

When the site's URL matches the URL regex in the webinject, Dridex will inject another “script” tag into the original response from the bank. This will cause the browser to issue a request for the JavaScript script mentioned in the “src” ("scripts/contextprov23.js").

As a result, the request for the script is generated with the domain of the targeted site.

For example, if the targeted site was mybank.com, the request for the script that was generated would be "mybank.com/scripts/contextprov23.js".

When the request for this script is generated within the browser, it is intercepted by the malware's network hook and is passed to the redirection mechanism, as seen in Figure 5.

redirection directive

Figure 5: Dridex 301 redirection directive

When the requested script is checked against such a redirection directive and there is a match, the request for the script is dropped and the same script request is launched to a different domain (the “URI” directive), so the script is actually fetched from the fraudster’s server.

During the redirection mechanism, the VNC flag (part of the redirect directive in the malware configuration) is checked, and if it’s true, the VNC module is launched. This triggers the browser network hook to deliver a message to the Dridex worker module inside the explorer.exe process. This message signals the worker module to launch the VNC module.

The module “vnc_x32” (or “vnc_x64” for 64-bit systems) is responsible for the VNC functionality. It exports: “VncStartServer” and “VncStopServer” functions to operate this activity.

While the Dridex worker module inside the explorer.exe process receives the message to launch VNC, the “VncStartServer” function address is resolved and the appropriate function is called.

Static code analysis of a “VncStartServer” call:

vncstart 1

Figure 6: Dridex 301 VncStartServer static view

Runtime debugging view:

vnc 2

Figure 7: Dridex 301 VncStartServer runtime view

 

Once the VNC server is started, the fraudster is able to remotely connect and use the victim’s machine.

Tested MD5: f6a9835201d5cae894863a46bbf12d69

Mitigation

F5 mitigates online identity theft by preventing phishing, malware, and pharming attacks in real time with advanced encryption and identification mechanisms. F5 products and services complement your existing anti-fraud technologies, improving your protection against malicious activity and providing an encompassing defense mechanism.

F5 enables financial organizations working online to gain control over areas that were once virtually unreachable and indefensible, and to neutralize local threats found on customers’ personal computers, without requiring the installation of software on the end user side. This approach covers the entire install base. The entire solution is delivered from the F5 BIG-IP platform and therefore doesn’t require any integration or modification of the application.

Rounding out its offerings, F5 provides professional services and advanced research capabilities in the field of cybercrime including malware, Trojans, viruses, and more.

To learn more about F5 fraud protection, read the WebSafe datasheet as well as the MobileSafe datasheet.

To learn more about the F5 Security Operation Center, read the F5 SOC datasheet.